The present invention relates, in general, to plastic encapsulation of small electronic devices, and more particularly to flashless molding of axial leaded devices.
Many types of electronic components, such as resistors, capacitors, and diodes, are encapsulated in an electrically insulating plastic material with the terminal wires of the component projecting from the encapsulating material. The easiest and least expensive manner of encapsulating such components on a mass production basis is to transfer mold the encapsulating material around the components. A problem with transfer molding is the removal of the flash which is formed around each of the encapsulated components, including flash along a portion of the terminal wires. Although the flash is thin and brittle, it adheres to the terminal wires and is difficult to remove completely. Typically this flash must be removed by chemical means, an expensive and difficult process due to the chemicals required.
Among other requirements, a flashless mold design requires a tight fit between the terminal wires and the matching wire grooves in the mold. This tight fit makes accurate alignment of the terminal wires in the grooves extremely critical. A lead which is even slightly misaligned will be crushed and require that the part be scrapped. In addition the tight fit tends to hold the terminal wires in the grooves when the mold is opened after the molding process is completed, damaging devices which happen to stick to the top half of the mold and complicating the removal of all devices from the mold.
Clearly there is a need for a mold for axial lead devices which does not produce flash and which facilitates loading and unloading of the devices from the mold.